Coupling circuit



May13, 1947. IRaCARTER 2,420,354

' TRANSMITTER COUPLING CIRCUIT Original Filed Jan. 10, 1941 4 Sheets-Sheet 1 F119;! I IA AN TEN NA TRA NSM/TTER TRANSM. &

N0. 2 LOAD CIRCUIT TRANS/M. No.3

TkA NSM N0. 1

INVENTOR. PHIL/P 6'. CARTER BY g ATTORNEY.

May 13, 1947. P. s; CARTER 2,420,354

COUPLING CIRCUIT Original Filed Jan. 10, 1941 4 Sheets-Sheet 2 T IL II TRANSMISSION LINE PHIL 5. CARTER ATTORNEY.

May 13, 1947.

TRANSM. 7,

TRANSM.

P. s. CARTER COUPLING CIRCUIT Original Filed Jan. 10, 1941 Lona,

TRANS/14. 7'2

4 SheetsSheet 3 D/POLE 7/1. TED 70 MAKE 0UAL ANGLES w/ 7/1 xy-z AXES FLA/V5 OF LOOP 77L7'ED 7'0 MAKE EQUAL ANGLES WIT/1 ALL THREE PLANES IN VEN TOR. P/l/L/P 8. CARTER ATTORNEY Patented May 13, 1947 COUPLING omourr Philip S. Carter, Port Jefferson, N. 'Y., assignor to Radio Corporation of America, a corporation'of Delaware Original application January 10, 1941, Serial No. 373,955. Divided and this application May 24,

1943, Serial No. 488,195

Claims.

This invention is a division of my copending application Serial-1N0. 373,955, filed January 10, 1941, now United States Patent 2,337,184, grantedDecember 21, 1943, and relates generally to a circuit for couplinga plurality .of sources of oscillation of different frequencies to a load in such manner thatthere is negligible, if any, interaction between the sources. Although the invention is particularly described with reference to an antenna system, it should be distinctl understood that this is mentioned in order to describe the principles of the invention, and not by way of limitation. N

One of the objects .of the present invention is to provide a radio system wherein two or three transmitters operating at different frequencies may be used simultaneously to excite the same load without interference with one another.

Another object is to provide a radio system wherein two or three transmitters of difierent frequencies maybe used simultaneously to excite different antennas from a common transmission line, without interaction between the transmitters. I

Other objects will appear from a reading of the following description.

In my copending application Serial No. 373,072, file'd'January 4, 1941, now U. S. Patent 2,357,314, granted September 5,]1944, there is described a method of exciting different types of cavity resonators in such manner as to cause the existence inthe resonators simultaneouslyof two or three types "of waves. These types of waves are the fundamental modes of oscillation whose frequencies differ from one another by a predetermined percentage, depending upon the dimensions of the resonator. The manner in which the resonators are excited and the relations for determining the dimensions or" these resonators are described in some detail in this copending application, for which reason it is believed necessary to repeat-therein only so much ofthe theory of operation set forth in my copending application which is necessary for an understanding of the principles involved inthe present invention. Although thepresent invention merely describes the use of rectangular prism resonators shown and described in more detail in connection with Figs. 1 and 2 of my 'copeno mg application, it should be understood that these resonators are illustrative of the various types of resonators which can be used 'andthat, if desired, the other types of resonator shown in my cop'endin'g applicationcan also be uSedtO obtain the resultsof the-present invention, provided that the same considerations described in my' copending application be adhered to. v

A better understanding of the "invention may befhad by referring to the following description, which is accompanied by a drawing wherein Figs. 1 to 4, inclusive, and .6 illustrate five different embodiments of the invention employing rectilinear pri'sm hollow resonators; andFig. 5 illustrates another embodiment of thej'invention employinga circular cylinder resonator. g V

.Fig. I shows one manner inwhich two trans mitters, labeled I and 2 respectively, can be employeds'imultaneously to excite a commonload (here shown by way of example as an antenna A) over a common transmission line T'L. with negligible or no interaction between the transmitters. In this figure, transmitters I and 2 are shown exciting a rectangular cavity resonator in such manner that there is caused to exist in the resonator two fundamental modesof oscillation whose frequencies correspond. respectively to the frequencies of the two transmitters. This resonator is generally of the form described in Fig. 2 :of my U. S. Patent 2,357,314, supra, and its dimensions are so cho'senthat the fundamental'mo'des of oscillationwill have frequencies which. differ from each other by the desired amount. The cavity resonator is shown as having sides a, b and 0, respectively parallelvto the axes :r, y, and z. The transmitter I is coupled to the resonator by means of a transmission line TL which enters the side L at its center toterminate in a small dipole m within the resonator. The axis of the dipole m is arranged parallel to the y axis and excites in the resonator a standing Wave oscillation in which the electric field is entirely horizontal and parallel to the y axis. The transmitter 2 isconnected to a transmission line 'TL" which enters the side F of the resonator at its center to terminate in a dipole n within the resonator. The axis of dipole n is arranged to be vertical and parallel with the z axis, so that it excites a standing wave in the resonator in which the electric force isentirely vertical. The resonator is so designed thatthe wave whose electric field is parallel to the gains has a .fundamental mode of oscillation whose frequency corresponds to the frequency of the transmitter 1., while the type of wave whose electric field is parallel to the z axis has a fundamental mode of oscillation-whose frequency corresponds to that of transmitter 2. It should also beunderstood that the dipoles m and n as arranged iniFig. .1 cannotexcite any other types of waves than those in which the electric fields are respectively parallel to the y and z axes. In view of this, it will be apparent that the standing waves produced in the resonator by the dipoles m and 11. are independent of each other and hence do not interact upon each other. Because of the perpendicular positioning of the dipoles m and n with respect to each other, there is no direct coupling between these dipoles. The fundamental natural wavelength y of the oscillation produced in the resonator by the dipole m and having its electric field parallel to the y axis is given by the relation 2ac -vm The fundamental natural wavelength AZ of the oscillation produced in the resonator by the dipole 11. whose electric field is parallel to the axis is given by the relation 2ab /dg+b2 By properly proportioning the dimensions of the sides of the resonator, the natural frequen-.

cies of the two modes of oscillation can be made to have any desired value. The output of the resonator of Fig. l is taken by a transmission line T'L which enters the face R at the center thereof and which is terminated in the resonator in a dipole p which is given a slope of 45 to the horizontal and lies in a plane parallel to the face R. The axis of the dipole p makes equal angles of 45 with the directions y and z, and its plane is perpendicular to the direction :11. With this arrangement, the dipole p will be excited equally by the electric field from both modes of oscillation of the resonator. The output transmission line T'L connected to the dipole 11 will carry the energy from the resonator to the load, here shown as an antenna A.

The coupling of the three transmission lines TL, TL and T'L to the waves in the resonator is kept quite small by using short dipoles m and n for excitation and also a short dipole p for the output. This results in very sharp resonance curves and prevents coupling between dipoles m and n indirectly by way of dipole p.

, Fig. 2 shows a system similar to that of Fig. 1, except that three transmitters 1, 2 and 3 of different frequencies are employed to simultaneously feed a load circuit A, such as an antenna, by way of a cavity resonator. Here the resonator is designed to have three natural fundamental modes of oscillation which correspond with the respective three frequencies of the transmitters I, 2 and 3. This resonator is similar in form to the cavity resonator of Fig. 1 of my copending application, supra. This resonator has three different principal dimensions. Transmitter I is connected to transmission line TL, in turn coupled to the dipole q which excites the resonator in the mode where the electric field is parallel to the :c axis. Transmitter 2 is connected to the transmission. line TL in turn terminated in the dipole s which excites the resonator with a wave having its electric field parallel to the y axis. Transmitter 3 furnishes excitation to the resonator by way of transmission line T'L and dipole t, the latter producing a wave having its electric field parallel with the z axis. All three transmission lines from the transmitters I, 2 and 3 enter the cavity resonator through different faces thereof at the respective centers thereof. The output energy is derived from the dipole u which is so positioned that its axis makes 60 cavity resonator of Fig. 2.

equal angles with the directions of the three coordinate axes :22, y and z. This is accomplished by slanting the dipole u so that its direction angle is 54.7" to the three directions a, y and a. By arranging the dipole u to have equal angles to the three directions at, y and 2, we are able to derive equal excitation from all three types of waves in the resonator. By changing this angle somewhat so that diiferent angles are made hetween axes of the dipole u and the directions at, y and 2, we are able to derive different excitations from the three waves within the resonator. The output transmission line T'L, which is coupled to the load A, which might be an antenna or any other suitable circuit, enters the resonator at one corner.

In Fig. 2 the three fundamental natural wavelengths Ax, A xz corresponding to the three modes of oscillation in the resonator wherein the electric field is parallel to the x, the y and the z axes,

respectively, are given by the following relations:

25 If these equations are solved under the assumption that \y I\Z, there is obtained the following relations which give the lengths of the three sides of the cavity resonator for any particular three frequencies.

M1,), z z z u'* y. It will be noted that the operation of the circuit 40 of Fig. 2 is similar to that of Fig. 1 except, so to speak, for the addition of a third transmitter which excites a third fundamental frequency in the resonator.

' Fig. 3 shows another embodiment of the present invention wherein three transmitters of different frequencies simultaneously excite a resonator V to produce three fundamental modes of oscillation whose frequencies correspond to the frequencies of the transmitters, the output from the resonator V being fed over a transmission line T"L" to another cavity resonator W in such manner that three different loads, such as antennas I, 2' and 3', may be excited from the resonator W. In this embodiment, it is desired that 5 the three loads I, 2' and 3 be excited respec- .65 fundamental modes of oscillation set up in the resonator V. The three fundamental frequencies of oscillation derived from cavity resonator V are fed by means of transmission line T"L into one corner of the cavity resonator W to causethe production of three fundamental modes of oscillation in cavity resonator W corresponding to the three frequencies in the line T"L". The dipoles in resonator W associated respectively with the loads I, 2' and 3' are so arranged that they each derive from the cavity resonator the desired frequency. It should be notedthat the output dipole u for resonator V is so arranged that its axis makes equal angles with the directions of the three coordinate axes of cavity r so at r V. and the input dipole in of the cavity resonator W is similarly arranged that its axis makes eq al angles with the directions at the three coordinate axes of the resonator W. The transmission. line 'I "'L" connecting the ouput dipole of cavity Iss0, nator V and the input dip l r avity resonator W enters each of these cavity resonators at a corner. as shown. The transmission lines extending from the transmitters and from the loads to the cavity resonators V and W respectively enter these resonators at the centers of the different faces in the same: manner as the transmission lines of Fig. 2 enter their associated cav ity resonator.

In practice, it is often desired to operate a sound transmitter and television transmitter'on the same antenna. The band width of a television signal may be of a-substantial percentage of the carrier and one ty e of wave alone in a cavity resonator may result in an insufiicient band width. Under such conditions, the resonator of Fig. 2 may be arranged so that the television transmitter, let us say transmitter 1, excites two types of waves in the resonator, the fundamental natural frequencies corresponding to said waves being made to differ by approximately two-thirds of'the' frequency band. The desired result is accomplished by properly proportioning the sides a, b and c and arranging the dipole q differently from that shown in Fig. 2 and in such manner that it makes equal angles with the m and y axes. Such an arrangement is shown in Fig. 4, wherein T2 is a television transmitter feeding dipole q, making equal angles of 45 with the a: and y axes, and T1 is a sound transmitter, feeding dipole t. The method of obtaining the desired band width has been more fully described in my U. S. Patent 2,357,314. Dipole s and transmitter 2 of Fig. 2 are not used in the system of Fig. 4. Transmitter 3 of Fig. 2, which feeds dipole t, corresponds to the sound transmitter T1 of Fig. 4 which excites, by means of dipole t, a wave whose electric field is entirely vertical and thus completely independent of the horizontal fields excited by the television transmitter. Dipole U, which is coupled to the load, is tilted to make equal angles with the :c, y and z axes.

It should be understood that other forms of cavity resonators may be used instead of the rectilinear prism hollow resonators shown in the figures. For the two frequency scheme of Fig. 1, the rectangular resonator may be replaced with a circular cylinder resonator (as shown in Fig. 5) or by a resonator whose form is either a prolate or an oblate spheroid. In place of the resonators of Fig. 2 and Fig. 3, a resonator in the form of an elliptic cylinder or in the form of an ellipsoid may be substituted. The properties of these other forms of resonators have been discussed in detail in my copending application Serial No. 373,072 supra. If desired, concentric lines may be used for feeding the cavity resonators, the excitation for the cavity resonator then being obtained by projecting the center conductor of the concentric line into the cavity resonator to an extent sufiicient to give the desired coupling.

If desired, loops of wire 'may be used in Figs. 2 and 3 in place of the dipoles. One such arrangement employing loops of wire as coupling elements is shown in Fig. 6. Due consideration must "6 hegiven-to the type of waves which can be 183- cited-bya particular loop. Fora clearer cinderstanding of these considerations which-:must be studied, reference is :made to my U. S. Patent 2,357,314..- supra, which teaches how "aloop can be substituted for a dipole'antenna in a cavity resonator of the type with which we are here concerned,- in order to achieve the desired results. As a generalization, it can be stated briefly that if the plane-nitric loop is' perpendicular to the axis it, this loop can excite waves whose electric fields are either in t e i l r adirections and whose natural wavelengths are given by therelations:

7 H 2m: w 2ab i/T re? t tee If the plane of the loop is perpendicular tothe y axis. this loop-can excite waves whose electric fields are either in the a: are directiongand whose natural Wavelengths are given by the relations:

If the. plane of the loop is perpendicular to the z axis,'.thl's loop ean excite waves whose electric fields are either in the ct or y directions and whose natural wavelengths are given by the relations:

212.0 2M n/Win" 1m If theplanes of the three input loops are mutually perpendicular and the loops are each fed with a different frequency (as shown in Fig. 6), the reaction between the transmitters will be negligibly small. The three loops fed by transmitters T1, T2 and Ta enter the resonator at positions at or close to the centers of the three faces of the resonator. The loop u feeding the load is tipped so that, its plane makes equal angles to the planes corresponding to the three faces of the resonator. In other words, a line perpendicular to the plane of this loop should make equal angles with the x, y and z axes. The loop for transmitter T1 excites the mode of oscillation wherein the electric field lines are parallel to the z axis and the magnetic field lines form complete circuits lying in planes parallel to the 03-11 plane. The loop for transmitter T2 excites a mode of oscillation wherein the electric field lines are parallel to the y axis and the magnetic lines form circuits lying in planes parallel the :n-z plane. The loop for transmitter T3 excites a third mode of oscillation wherein the electric field lines are parallel to the x axis and the magnetic lines form complete circuits in planes parallel to the 11-2 plane.

The term different types of waves is used in the appended claim to designate waves whose electric fields are principally in different directions. Thus, in considering a hollow rectangular prism resonator the electric fields are at right angles to one another for the two or three different types of waves, while in a hollow ellipsoidal resonator the electric fields are principally in the directions of the three principal axes of the three principal cross-sections.

What is claimed is:

1. In combination, a plurality of sources of oscillations of difierent frequencies, a load, a cavity resonator interposed between said sources and said load, the dimensions of said resonator being such as to enable the production therein of modes of oscillation whose frequencies differ by a predetermined amount, loops of wire within said resonator coupled to said sources and so arranged as to excite in said resonator different types of waves for the different frequencies of said sources, and an element within said resonator coupled to said load and so arranged as to pick up energy from the different types of waves produced within said resonator by said loops of wire.

2. In combination, a plurality of sources of scillations of difierent frequencies, a load, a cavity resonator interposed between said sources and said load, loops of wire within said resonator coupled to said sources and having their planes mutually perpendicular so as to excite in said resonator different types of waves for the different frequencies of said sources, and another loop within said resonator coupled to said load and having its plane arranged to pick up energy from all the different types of waves produced within said resonator.

3. In combination, a plurality of sources of oscillations of different frequencies, a load, a cavity resonator interposed between said sources and said load, loops of wire within said resonator coupled to said sources and having their planes mutually perpendicular so as to excite in said resonator different types of waves for the different frequencies of said sources, and another loop within said resonator coupled to said load and having its plane arranged so that a line perpendicular thereto makes substantially equal angles to the principal directions of said resonator.

4. In combination, a plurality of sources of oscillations of different frequencies, a load, a cavity resonator interposed between said sources and said load, the dimensions of said resonator being such as to enable the production therein of modes of oscillation whose frequencies differ by a predetermined amount, elements within said resonator coupled to said sources and so arranged as to excite in said resonator different types of waves for the different frequencies of said sources, and a loop of wire within said resonator coupled to said load and so arranged as to pick up energy from the different types of waves produced within said resonator by said elements.

5. In combination, a plurality of sources of oscillations of different frequencies, a load, a cavity resonator interposed between said sources and said load, loops of wire within said resonator coupled to said sources and so arranged as to excite in said resonator different types of waves for the different frequencies of said source, and another loop of wire within said resonator coupled to said load and so arranged as to pick up energy from the difierent types of waves produced within said resonator by said loops or wire.

PHILIP S. CARTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,199,083 Schelkunofi Apr. 30, 1940 2,281,550 Barrow May 5, 1942 2,337,184 Carter Dec. 21, 1943 

